Peugeot 205 T16 changed it all

Peugeot 205 T16 was designed by Andre De Cortanze (with Jean Claude Vaucard as Chief Engineer and responsible of chassis design) to counterattack 1983 Audi Quattro dominance with similar arguments: four wheel drive and a turbocharged engine, mounted in a central, transversal disposition, and a very light tubular chassis. Once homologated (see Homologation Form here), the car quickly impressed in the championship by leading the first rally in which it took part (Tour de Corse 1984), and got an impressive performance of 9 victories in 14 participations, in the hands of Ari Vatanen and Timo Salonen during 1984 and 1985.

But it was born with significant aerodynamic problems, which were quickly detected since its first appearance, the 1983 Trophée Jean François Piot. J.P.Nicolas took the wheel and he reported lack of aerodynamic downforce and unstable behaviour during flights after road jumps.

It was too late to fix, as the production of 200 cars for homologation was already on. The car was only fitted with a small spoiler at the end of the roof, so big changes had to be prepared for the Evolution 2 of the car, to be launched in 1985. And other manufacturers also started preparing their new cars (Audi, Lancia, Ford, Citroen, MG) for the 1986 championship, to stop Peugeot avalanche, leading to a revolution, in terms of aerodynamic devices.

Mazda factory had no budget and no interest in preparing a car for the World Rally Championship, so Mazda Rally Team Europe had to take the initiative, and they developed a tough Mazda RX7 group B car, with a (rotary) Wankel engine, which got its best results in Acropolis Rally. The car was fitted with a big and well integrated rear spoiler, which included an oil cooler inside.

I.Carlsson/M.Melander, Mazda RX7, Acropolis Rally 1985, 3rd

Renault launched its group B car in the spring of 1985, under the name of Renault 5 Maxi Turbo. It was an evolution of the 5 Turbo with increased power and bigger spoilers. The purpose was to create the fastest two-wheel drive rally car, but it was quickly overcome by more effective, turbocharged four-wheel drive vehicles (see Homologation Form here). Jean Ragnotti drove the car to his only victory in the Championship in the first appearance, at the 1985 Tour de Corse.

J.Ragnotti/G.Thimonier, Renault 5 Maxi Turbo, Tour de Corse 1985, 1st

Due to the limitation of two-wheel driving, the car only reappeared in the Championship in the 1986 Tour de Corse, where it finished second. However, it was more successful in those National Championships based on asphalt rallies, such as in France and Spain,